This invention relates to the splicing of webs from a succession of web rolls while the webs are in motion so that web can proceed uninterruptedly to a web consuming machine, such as a printing press. It relates more particularly to a method and apparatus for closely matching the speeds and positions of the webs being spliced at the time of the splice.
The providing of an uninterrupted supply of web is important in many industries, particularly in the printing industry. Today's high speed printing presses print on web, i.e. paper, cloth, etc., drawn from a roll rotatably supported by a roll stand located upstream of the press. In order to avoid having to shut down the press each time a web roll expires, a splicing mechanism is invariably incorporated into the roll stand to enable the trailing end of the expiring web to be spliced to the leading end of the web on a new roll.
Modern day presses can turn at very high speeds and thus they consume web at a high rate, e.g. in excess of 2000 feet per minute (fpm). Consequently, in order for the printing operation to proceed with maximum efficiency, it is essential that the splicing of one web to another occur in a minimum amount of time and with a minimum wastage of web.
It is also critical that each splice be made and be essentially perfect to avoid large tension upsets and downstream web jams which can cause a web break, necessitating stoppage of the press or other web consuming machine.
Speed match splicing of one web to another can be accomplished at line speed, i.e., the speed of the press or other web consuming machine, or at some lesser speed. In the former case, prior to making a splice, the ready or fresh roll, which may be supported on a rotatable turret, is accelerated so that its surface speed substantially matches the speed of the running web which travels at a selected line speed. When splicing at a lesser speed, the new or ready roll is accelerated to a selected speed less than line speed and the running web is decelerated to that speed in anticipation of the splice. In both cases, just before the running roll expires and when the speeds of the two webs are ostensibly matched, the splice is made between the trailing end of the running web and the leading end of the web on the ready roll. In the latter case, after the splice, the ready roll is accelerated up to line speed and during the time the running web roll was slowed, the web consuming machine draws web from a web store such as a festoon or accumulator located between the splicer and the web consuming machine. That web accumulator is refilled with web following each splicing operation.
In speed match splicers such as this, prior to each splicing operation, the leading end of the web on the ready roll must be prepared for the splice. Such preparation involves trimming the leading end of the web on the ready roll so that it is straight, V-shaped or W-shaped depending upon the size of the roll, and temporarily "tacking" that end to the underlying web convolution on the roll by means of short adhesive strips spaced along the leading end of the web and oriented perpendicular thereto. The tacking of the leading end to the remainder of the roll can also be accomplished with appropriate releasing adhesive spots applied to the undersurface of the leading edge margin of the web.
The splice preparation procedure invariably also involves the application of a straight, V-shaped or W-shaped double face splicing tape to the leading edge margin of the web on the ready roll. That adhesive presents a sticky or tacky surface to the running web. In lieu of tape, adhesive lines or spots may also be used for this purpose.
In the typical speed match splicer, the actual splice is effected by pressing the running web momentarily against the surface of the ready roll at the adhesive area thereon after the running web and the ready web roll surface have been speed matched as noted above. The two webs become pasted together or spliced as soon as the splicing tape or adhesive area is rotated into engagement with the running web. Immediately thereafter, a knife is actuated to sever the running web just behind the splice, thereby separating the running web from its nearly empty roll core, leaving the ready roll to supply the continuing needs of the web consuming machine.
While the above-described prior splicers have operated satisfactorily at reasonably high press speeds, i.e., up to 2000 fpm, as these speeds approach 3000 fpm, certain problems manifest themselves, many of which are traceable directly or indirectly to the techniques used heretofore for measuring the relative speed and position of the two webs being spliced to effect the speed and position matches prior to splicing.
More particularly, the speed and position of the running web are usually more or less constants because the web is being drawn under tension within the press or other machine which runs at a fixed line speed. The speed of that web can be monitored accurately, e.g., by a tachometer or shaft encoder responding to the surface speed or angular velocity of a fixed diameter guide roller around which that web is trained. However, monitoring the speed of the ready web prior to splicing is another matter altogether. The speed of the ready web at that time is actually the surface speed of the ready web roll because, prior to the actual paste of the two webs, the leading edge margin of the ready web is "tacked" to the underlying web convolution on that roll as noted above.
Conventionally, the surface speed of a ready web roll may be monitored by a tachometer rotated by a follower wheel which rides on the surface of the ready roll as that roll rotates. The signals from the tachometer may be compared with the signals from the guide roller tachometer which monitors the surface speed of the running web to produce a speed difference signal. This difference signal can be used to speed up or slow down the ready web roll if the speed of the running web is the speed reference. Alternately, the difference signal can be applied to regulate the speed of the running web if the ready roll speed is used as the reference. However, the use of a tachometer wheel results in there being a gap in the splice to the running web. That is, conventionally a gap is provided in the adhesive tape or area at the leading edge of the ready web to provide clearance for the tachometer wheel. This is to prevent the wheel from sticking to the adhesive and to prevent the wheel from bouncing were it to encounter the edge of the adhesive tape.
In those splicers which use roll surface-engaging accelerating belts to accelerate the ready roll, the surface speed of the ready roll may also be monitored by a tachometer which measures the speed of the belts. Here again, however, gaps in the splicing tape or area are present to provide non-adhesive areas where the belts engage the web roll.
In both of the above splicers, the presence of such adhesive gap(s) results in there being gap(s) in the splice to the running web. Resultantly, after splicing, as the web travels at high speed through the press, windage at the surface of the web can lift the leading edge of the former ready web at the splice gap(s) so that that edge tends to catch or jam in downstream printing couples, causing damage to the rollers and/or a web break.
Also, a roll of web is hardly ever a perfect cylinder; it has surface bumps and eccentricity. For example, it is not unusual for, say, a 50 inch diameter web roll to be out of round by as much as 1/2 inch. Therefore, if that roll is rotated at a fixed angular velocity, the surface speed at the high point on the roll will be appreciably greater than the surface speed at the low point thereon. For the above roll, this translates to a 1-2% speed difference or variation at the roll surface.
Therefore, a wheel or belt-driven tachometer really measures the average surface speed of the ready web and, conventionally, it is that average speed that is compared to the running web speed to achieve a so-called speed match. In actuality, however, the surface speed of the web roll where the paste to the running web is actually made, i.e., at the web edge margin carrying the splicing tape or adhesive area, may be appreciably different from that detected average speed. As a consequence, when the paste is made, there may be an appreciable web speed mis-match, i.e., in the above example of as much as 1-2%, depending upon where the tape is located around the roll axis. While such poor accuracy can be tolerated at lower web speeds, it cannot at web speeds approaching 3000 fpm. At those higher speeds, a speed mis-match of that size can result in a missed splice or a wrinkled or otherwise defective splice which can damage downstream printing couples and/or cause a web break.
The surface speed of a web roll may also be determined by measuring the angular velocity of the roll using a shaft encoder operatively connected to one of the chucks supporting the web roll. Multiplying that angular velocity and the radius of the roll yields the surface speed of the roll. However, as just described, the roll radius may vary around the axis of the roll due to irregularities in the roll. Conventional techniques for measuring roll radius, actually measure the radius of the highest point around the roll axis or perhaps the average radius (i.e., the average of the highest and lowest points around the roll axis). Thus, that measurement does not necessarily reflect the radius of the roll at the location where the splice is to occur, i.e., at the web leading edge margin carrying the splicing tape or adhesive area. Therefore, that speed measuring technique has the same disadvantages noted above in terms of defective and missed splices at high web speeds.
While a missed splice may not seem to be a particularly momentous event, it should be bourne in mind that for press speeds around only 2000 fpm, the press industry has calculated that, on average, 1% of the splices are missed and that each missed splice costs in the order of $400.00 due to web wastage and downtime. Obviously, at higher speeds, the number of misses and the monetary loss would be even more. Therefore, a splicer with the ability to reduce the number of splice misses by only 0.5% would be considered extremely important to the industry.
When splicing two webs, it is also important that the lateral positions of the webs be matched; i.e., the corresponding side edges of the two webs should be aligned. The usual procedure for accomplishing this is to monitor the edges of the running web and the ready web roll using known optical, mechanical or pneumatic web edge sensors. Then, with one of the webs being the reference, a difference signal is developed and applied to control the lateral position of the carriage supporting the roll letting of the other web until the two webs are aligned.
Here again, this procedure does not take into account the fact that a web roll is hardly ever a perfect cylinder. It may be racked such that its ends are not exactly perpendicular to the roll axis. Consequently, when the roll is rotated, its ends may wobble. For a web roll 50 inches in diameter, the wobble can be as much as .+-.3/16 inch. Therefore, when the edge of the web roll is being sensed for web alignment purposes, the sensor will actually measure an average roll edge position which may or may not be the actual position of the roll edge where the splice is made to the running web, i.e., at the splicing tape or adhesive area on the ready roll. For example, if the leading end of the ready web and splicing tape thereon are at the laterally outermost position o the tilted end of the roll and the matching of the web positions is based on the average lateral position of the roll, when the leading end of the ready web is actually pasted to the trailing end of the running web, the side edge of that leading end may project laterally beyond the corresponding edge of the running web by as much as one-half of the roll end wobble. Such a projecting edge margin will extend outside the normal web running zones on downstream web guide rollers and pick up high tack ink residue that can jam in downstream printing couples causing roller damage, web tension upsets and/or a web break.
It would be desirable, therefore, if there existed a technique for measuring the speed and lateral position of a web roll so as to achieve a more or less exact web speed match and web edge position match at the instant of the paste or splice of a ready web to a running web. This would make it possible to minimize the incidence of defective and missed splices and web misalignments that typically cause problems in downstream web consuming machines, such as high speed presses.